1. Field of the Invention
The present invention relates to a communication terminal that selects an optimal reception system and reduces reception failure.
2. Description of the Related Art
In recent years, services for delivering video and audio contents, etc. to a plurality of users by broadcast via a wired broadband circuit, such as Asymmetric Digital Subscriber Line (ADSL) and Fiber-To-The-Home (FTTH), are becoming popular. IP multicast technology, represented by Internet Group Management Protocol (IGMP), is used in multicast services such as these.
The IP multicast technology is an extremely effective means in one-to-many communication where the same contents are transmitted simultaneously to a plurality of receivers. Thus, the use of this technology is growing, not only in the field of wired communication, but also in the field of wireless communication. Technology as such is, for example, disclosed in the Japanese Laid-open Patent Publication No. 2001-308856.
In addition, as disclosed, for example, in the publication of The Institute of Electronics, Information and Communication Engineers Journal November 2002, Vol. J85-B, No. 11, p 1823 to 1824, a communication technology, referred to as reliable multicast, that enhances reliability through the combined use of one-to-one unicast communication and one-to-many multicast communication is also known.
A reason for the combined use of multicast communication and unicast communication in the reliable multicast system is because multicast communication is favorable at times and unicast communication is favorable at other times depending on the mobile radio environment of individual terminals. For example, in a one-to-many, single-direction communication such as the multicast communication, the transmission rate is generally unilaterally decided by the transmitting-end. In this case, the probability of failure is high when multicast reception is being carried out because a communication terminal that has a weak received signal strength indicator and is strongly influenced by the effects of error factors, such as noise, interference, and attenuation. Therefore, it is preferable to perform reception for a terminal in a degraded mobile radio environment using the transmitting-end to acquire negotiation by one-to-one unicast and establishing communication suitable for the reception mobile radio environment of that terminal.
However, the method of combining and using multicast communication and unicast communication in the reliable multicast system is unique. In other words, when a reception terminal performs multicast communication, communication is performed through a predetermined combination regardless of the terminal being in an environment with high reception failure probability and as a result, reception failure may occur.